1. Field of the Invention:
The present invention relates generally to a nuclear fuel rod loader for pulling fuel rods into a fuel assembly skeleton and, more particularly, is concerned with a nuclear fuel rod loader having a rod gripper design which avoids snagging spacer grid dimples during the rod loading operation.
2. Description of the Prior Art:
In the typical nuclear reactor, the reactor core includes a large number of fuel assemblies each of which is composed of top and bottom nozzles with a plurality of elongated transversely spaced guide thimbles extending longitudinally between the nozzles and a plurality of transverse support grids axially spaced along and attached to the guide thimbles. Also, each fuel assembly is composed of a plurality of elongated fuel rods transversely spaced apart from one another and from the guide thimbles and supported by the transverse grids between the top and bottom nozzles. The fuel rods each contain fissile material and are grouped together in an array which is organized so as to provide a neutron flux in the core sufficient to support a high rate of nuclear fission. The reactor also has control rods which can be inserted into the guide thimbles to control the fission reaction. The fission reaction releases a large amount of energy in the form of heat. A liquid coolant is pumped upwardly through the core in order to extract some of the heat generated in the core for the production of useful work.
In the construction of a fuel assembly, the guide thimbles are affixed to the grids to form a fuel assembly skeleton. Then, the fuel rods are loaded into the skeleton, passing through the cells of the grids. Typically, a fuel rod loader is used which pulls the fuel rods into the grids. The loader has a rod gripper which is inserted through the skeleton, coupled to the end plug of a fuel rod, and then withdrawn, pulling the attached fuel rod into the skeleton. Finally, the top and bottom nozzles are affixed to the skeleton to complete the fabrication of the fuel assembly.
A typical nuclear fuel rod loader is disclosed in U.S. Pat. No. 4,297,776, hereby incorporated by reference. The loader described therein uses a rod gripper which couples to an external circumferential groove on a fuel rod end plug.
Westinghouse U.S. patent application Ser. No. 797,331 entitled "Improved End Plug With Truncated Tapered Leading End Configuration" by D. A. Boatwright and W. Widner, filed 11/12/85, discloses a fuel rod gripper 46, as seen in FIG. 4, for loading (pulling) a nuclear fuel rod into a fuel assembly skeleton (see page 8, line 35 to page 9, line 18). The figure shows an enlarged, finger slot stress-relieving keyhole. This rod gripper (having three or four fingers), and including a version with the enlarged keyhole counterbored, has been in use for more than one year. Grippers of this design have a tendency to have their closed slot end snag on a grid dimple during insertion of the puller into the fuel assembly skeleton. This was true even when the keyhole was countersunk. Bent and broken-away dimples have occurred.